Hydraulic ejector control mechanism for earthmoving scraper



Aprii 11, 167 J A,JUNCK ETAL HYDRAULIC EJECTOR CONTROL MECHANISM FOR EARTHMOVING SCRAPER Filed July 2, 1964 2 Sheets-Sheet 1 INVENTORS JOHN A. JUNCK BY JOSEPH KOKALV ATTORNEYS April 11, 1967 A JUNK ETAL 3,313,050

HYDRAULIC EJECTOR CONTROL MECHANISM FOR EARTHMOVING SCRAPER Filed July 2, 1964 2 Sheets-Sheet 2 25 RESERVOIR INVENTORS JOHN A. JUNCK BY JOSEPH KOKALY WWI/Z ATTORNEYS United States Patent 3,313,050 HYDRAULIC EJECTOR CONTROL MECHANISM FUR EARTHMOVIN G SCRAPER John A. lunch and Joseph Kokaly, Joliet, Ill., assignors to Caterpillar Tractor (10., Peoria, Ill., a corporation of California Filed July 2, 1964, Ser. No. 379,838 2 Claims. (Cl. 37-129) The present invention relates to improvements in the hydraulic circuitry of an earthmoving scraper in which the scraper components are adjusted hydraulically and pertains more particularly to the circuit which controls the ejector.

Hydraulically controlled scrapers with ejectors of the type which are advanced forwardly through the scraper bowl to eject its contents employ horizontally disposed cylinders or hydraulic jacks. These jacks have a necessarily long stroke and are therefore provided with large diameter piston rods to obtain adequate column strength. This results in a much greater volumetric capacity, sometimes as much as 100%, in the head end of the cylinder than in the rod end. This is undesirable for several reasons. First, when pump flow is directed to the rod end of the cylinder to retract the ejector after it has been used to eject a load, the cylinder piston has to eject the much greater volume of fluid back through the lines and control valve to the tank. The resistance to flow of this large volume is imposed on the pump which then develops high pressure and utilizes horsepower unnecessarily. This usually takes place after discharging a load and when all available power is desired to accelerate the progress of the machine out of a fill pit and on the return leg of its cycle. In fact tests show that as much as 175 horsepower is dissipated in this manner.

Furthermore, the filter of such hydraulic systems is conventionally located in the low pressure line between the control valves and the reservoir and the high volume return flow opens the filter bypass valve and the oil is returned directly to the reservoir. This is particularly undesirable because the ejector jack is horizontally disposed and notoriously a point of collection of foreign matter which will be returned to the reservoir and recirculated through the system if the filter is bypassed.

It is the object of the present invention to overcome the aforementioned disadvantages and to provide a control circuit for a scraper ejector in which operating speeds and pressures during return stroke are maintained at levels sufficiently low to insure satisfactory operation.

Further and :more specific objects and advantages of the invention and the manner in which it is carried into practice are made apparent in the following specification by reference to the accompanying drawings.

In the drawings:

FIG. 1 is a view in side elevation of a tractor-scraper combination of the type in which the present invention is employed; and

FIG. 2 is a schematic diagram of a hydraulic circuit for actuating an ejector embodying the present invention.

The machine illustrated in FIG. 1 is of a conventional type in which a tractor, generally indicated at 10, draws a scraper 11. The scraper bowl 12 is pivotally supported about the axis 13 of its wheels and the forward end of the scraper can be raised and lowered by a jack illustrated at 14 so that it will be filled when a cutting edge 15 engage-s the earth. An apron 16 pivoted to the bowl as at 17 normally closes the forward end of the bowl and may be opened and closed by a hydraulic jack such as illustrated at 18.

The ejector with which the present invention is used is in the form of a plate which closes the rear of the bowl 12 as indicated at 20 and is arranged to be advanced for- 3,313,050 Patented Apr. 11, 1967 ice wardly as by an ejector jack shown in dotted lines at 21. Forward movement of the ejector when the apron is in its open position urges the contents of the bowl out through the forward end thereof. Because of the necessary length of the ejector jack and unusual length of its stroke, the rod 22 of the jack shown in FIG. 2 is larger than that of most hydraulic jacks and occupies so much spacee within the cylinder that the volumetric capacity is greatly reduced and very low as compared to the volumetric capacity in the opposite or head end of the cylinder. The present invention is directed to the elimination of disadvantages which arise from this great difference in volumetric capacity.

Generally speaking, the circuit of FIG. 2 comprises a pump 24 which directs fluid from a reservoir 25 through a control valve generally indicated at 26 to either end of the ejector jack 21 depending upon the position of the control valve. The valve is shown in FIG. 2 in its neutral position. In order to introduce fluid to the rod end of the jack 21 for retracting the ejector after it has been actuated to eject a load, a spool 28 of the valve is adjusted to the left from the position shown to communicate fluid from the pump past a land 29 and through a line 30. If the full volume of the pump is directed to the rod end of the jack, the fluid in the head end of the jack which is greater in volume will, in returning through a line 32, the valve 26 and a line 33 to the reservoir, build up resistance requiring maximum effort of the pump 24 and utilization of horsepower far in excess of that required for the purpose of returning the ejector. To prevent this undesirable operation, the present invention provides a flow control mechanism to insure that a reduced but constant volume of fluid will be supplied to the ejector jack which is sufficient to return the ejector at a relatively slow rate. The amount of fluid which passes the land 29 is reduced by providing metering slots as shown at 35 through which the fluid passes when the spool is adjusted to the left from the position shown. A combination flow control and relief valve mechanism is provided by the valve structures 36 and 37.

Valve structure 36 includes a sleeve valve 38 controlling communication between the pump pressure side in spool valve '26 and the discharge line 33. A spring 39 loads the valve 38, biasing it toward the closed position shown, and it is further loaded by pressure on the discharge side of slots 35 which is being communicated to the ejector jack. This lower pressure is communicated to the chamber of spring 39 through a passage 40 and valve structure 37. A spool 42 in this valve is biased to a closed position by a spring 43 but opened by pressure to communicate fluid from a central bore 44 and a transverse bore 45 to a relief 46 in the spool and thence through a passage 47 to the spring chamber, the passage 47 having a restriction 48. Thus, a constantly regulated volume is maintained in the line leading to the ejector jack because the pressure on the downstream side of the slots 35 is constantly loading the sleeve valve 38 and the pressure differential across slots 35 is only of the magnitude required to overcome the force of spring 39 to open the valve and discharge excess oil toward the reservoir. A pressure relief valve 50 also contained in the valve assembly 36 protects the entire system by relieving excessive pressure and causing a drop in pressure in the chamber of spring 39 permitting the sleeve to open fully and discharge pressure to the reservoir. The restriction 48 creates a pressure differential on opposite sides of valve 38 when relief valve 50 is open.

It is necessary that the relief valve controlled by valve element 50 function at all times and in order that it will operate When the ejector is being advanced, pressure will be communicated to the chamber of spring 39. This is accomplished by a passage 52 which communicates with the line 47 when the spool 42 is in the closed position shown.

Since the present invention greatly reduces the rate of return flow from the ejector jack, it eliminates opening of a bypass valve shown at 55 in the return line to the reservoir. Thus, all return oil passes through a filter shown at 56.

What is claimed is:

1. In an earthmoving scraper having an earth receiving bowl, an ejector movable through the bowl to eject its contents, hydraulic power means including a cylinder with a piston and rod for actuating said ejector, a source of fluid under pressure, and valve means for directing fluid from said source to the head end of the cylinder to advance the ejector and to the rod end of the cylinder to retract the ejector, the improvement which comprises flow control means limiting the volume of fluid directed to the rod end of the cylinder to reduce the rate of return flow of fluid from the head end thereof, a bypass valve controlling communication between a pressure inlet port in the valve means and a return line to the source with pressure in the inlet acting on one end of the bypass valve, other valve means responsive to pressure in the rod end of the cylinder to communicate the cylinder pressure to a chamber at the opposite end of the bypass valve, and a spring in said chamber biasing the bypass valve toward a closed position, said other valve means having a second position communicating the pressure inlet port with said chamber when communication between the inlet port and the rod end of the cylinder is blocked.

2. The combination of claim 1 with a relief valve responsive to pressure in the chamber to permit opening of the bypass valve to direct the fluid from the source back to the source.

References Cited by the Examiner UNITED STATES PATENTS 1,943,061 1/1934 Douglas 6052 2,568,528 9/195'1 Welte l37-596.12 2,946,144 7/1960 Anderson 6052 ABRAHAM G. STONE, Primary Examiner.

A. E. KOPECKI, Assistant Examiner. 

1. IN AN EARTHMOVING SCRAPER HAVING AN EARTH RECEIVING BOWL, AN EJECTOR MOVABLE THROUGH THE BOWL TO EJECT ITS CONTENTS, HYDRAULIC POWER MEANS INCLUDING A CYLINDER WITH A PISTON AND ROD FOR ACTUATING SAID EJECTOR, A SOURCE OF FLUID UNDER PRESSURE, AND VALVE MEANS FOR DIRECTING FLUID FROM SAID SOURCE TO THE HEAD END OF THE CYLINDER TO ADVANCE THE EJECTOR AND TO THE ROD END OF THE CYLINDER TO RETRACT THE EJECTOR, THE IMPROVEMENT WHICH COMPRISES FLOW CONTROL MEANS LIMITING THE VOLUME OF FLUID DIRECTED TO THE ROD END OF THE CYLINDER TO REDUCE THE RATE OF RETURN FLOW OF FLUID FROM THE HEAD END THEREOF, A BYPASS VALVE CONTROLLING COMMUNICATION BETWEEN A PRESSURE INLET PORT IN THE VALVE MEANS AND A RETURN LINE TO THE SOURCE WITH PRESSURE IN THE INLET ACTING ON ONE END OF THE BYPASS VALVE, OTHER VALVE MEANS RESPONSIVE TO PRESSURE IN THE ROD END OF THE CYLINDER TO COMMUNICATE THE CYLINDER PRESSURE TO A CHAMBER AT THE OPPOSITE END OF THE BYPASS VALVE, AND A SPRING IN SAID CHAMBER BIASING THE BYPASS VALVE TOWARD A CLOSED POSITION, SAID OTHER VALVE MEANS HAVING A SECOND POSITION COMMUNICATING THE PRESSURE INLET PORT WITH SAID CHAMBER WHEN COMMUNICATION BETWEEN THE INLET PORT AND THE ROD END OF THE CYLINDER IS BLOCKED. 